dewhubst



RyJ. DBWHURST. SCREW BOLT PoR PASTENING RAILROAD CHAIRS.

NAAsl. Patented July 4,41865 Be it known thatLRICHARD `Hunsnof `the cityand county of New York Rioni). JAMES DnwHUns'r. or Nnw YORK, N. Y.

SCREW-BOLT FORAFASTENING RAILROAD-CHAIRS.

Specification of LettersPatent No. 48,531, dated July 4, 1865.

To all whom t may concern JAMES` DEW- other purposes where `the screw isintended to enter and hold in wood; and I do hereby declare that thefollowing4 is a full and eX: l act` description thereof, reference beinghad to theaccompanying drawings, Figures l and 2, in both of which`` y Ais the head of the bolt, here shown of the T form as now generally usedfor putting down railroad bars and chairs, but it may libe polygonal orof any other form desired. y .iB lis the shank of the `bolt of round bari iron, and c the screw, which may have any `desired form of thread butthe serrated form here` shown `is considered the best `adapted forholding in timber. Thisscrcw `maybe'inade tapering as shown in F ig. l,

" or` `spindle form` or'` cylindrical and gimlet pointed'as shown inFig. 2.

bolts complete and lit for use by forging the "screw thread thereonwhilehot, by a peculiar `modewhich` I have devised for that Myinventionconsists in producing such purpose and by which a rotative andlongitudinal movementbeing imparted `to. the bolt, the thread orAscrewzis gradually formed `and finished, commencing at the` point i ofthe `bolt and progressing onward to` the required extent: the displacedmetal from betweenthe threads being worked into the screw part of thebolt as the operation progresses, thereby` increasing that part of thebolt lengthwise andpreserving a con- Istant and unbroken relationshipbetween the body or central part of the boltand its sursize of iron, itsgreatercapacity for holding .l y in timber, and the comparativecheapness *Y of its product-ion. The screw thread in these `bolts beingproduced by forging, `the ma- "terial usually turned off from the `barto 550;

" `ing `worked intothe screw part of the bolt,

form the thread is ent-irelyeconomized, be-

whichsaving, in a bolt ofthe size shown in i `@the drawings, forms abouteighteen per cent.

of the `whole weight.

In relation y to the f matter of strength, it` is well known that ironis not as solid or as strong as the eX- terior portion of such bar,which exterior portion of the bar is usually turned off and wasted, asbefore observed when the thread is formed by chasing, thus leaving forthe body of the screw a portion of the bar which is of inferiorstrength. In a three quarter inch bolt, as shown in the cylindri- `calpart of C, in Fig. 2, a thread ofproper size to hold efficiently intimber should be cut in to the depth of one eighth of an inch, leavingthe central portion half an inch in diameter. The area of the crosssection of the bar is thus reduced from .4,417 to .1,963 of a 'squareinch, showing that five-ninths of the original substance of the bar hasbeen turned off and wasted in forming the thread, but as before stated,the interior portion thus left to form the body of the screw is ofcomparatively less strength than the eX- terior portion which was cutaway in forming the thread, and although such central portion forms thefour ninths of the Msubstance of the bar its strength is not more, inthe average run of bar iron, than one third the original strength ofsuch bar: when however', such screw thread is formed by forging, asdescribed, the interior portion becomes consolidated and sostrengthenedby the operation as to be equal in ordinary bar iron to about one halfthe strength Vof such bar; from which it fis manifest that forged screwsof a given size of iron are much stronger than chased screws of the samesize of iron, thereby enabling such bolts to more eiiciently resist thetorsion to which they are unavoidably subjected in penetrating timber.

The tapering form of screw shown in the drawing atFig. l, has also amaterial advantage over the screw of uniform diameter by reason of thegreater hold it takes in the timber, as I have experimentally'ascertained, having placed a chased screw of uniform diameter and aforged screw of tapering form, side by side in the same piece of ircseven per cent. in favor of the taper screwr the mode or processsubstantially as debolt.

Having thus described my improved screw boltfwhat I claim as myinvention, 5 and desire to reoure by Letters Patent is- Tlie bolt withthe screw part thereof formed substantially as described and by scribed,as a new article of manufacture.

RICHARD J. DEWHURST.

Witnesses ANDREW I. TODD, JOHN CooHRANE.

